Dark/light modulation of ribulose bisphosphate carboxylase activity in plants from different photosynthetic categories

Abstract

Ribulose bisphosphate carboxylase/oxygenase (RuBPCase) from several plants had substantially greater activity in extracts from lightexposed leaves than dark leaves, even when the extracts were incubated in vitro with saturating HCO3- and Mg2+ concentrations. This occurred in Glycine max, Lycopersicon escukntum, Nicotiana tabacum, Panicum bisulcatum, and P. hylaeicum (C3) P. maximum (C4 phosphoenolpyruvate carboxykinase) P. milioides (C3/C4); and Bromelia pinguin and Aanas comosus (Crassulacean acid metabolism). Little or no difference between light and dark leaf extracts of RuBPCase was observed in Titicum aestivum (C3) P. miliaceum (C4 NAD malic enzyme); Zea mays and Sorghum bicolor (C4 NADP malic enzyme) Moricandia arvensis (C3/C4); and Hydrilla verticillata (submersed aquatic macrophyte). It is concluded that, in many plants, especially Crassulacean acid metabolism and C3 species, a large fraction of ribulose-1,5-bisphosphate carboxylase/ oxygenase in the dark is in an inactivatable state that cannot respond to CO2 and Mg2+ activation, but which can be converted to an activatable state upon exposure of the leaf to light.